Method and apparatus for point cloud coding

ABSTRACT

An apparatus for point cloud decoding includes processing circuitry. The processing circuitry receives, from a coded bitstream for a point cloud, encoded occupancy codes for nodes in an octree structure for the point cloud. The nodes in the octree structure correspond to three dimensional (3D) partitions of a space of the point cloud. Sizes of the nodes are associated with sizes of the corresponding 3D partitions. Further, the processing circuitry decodes, from the encoded occupancy codes, occupancy codes for the nodes. At least a first occupancy code for a child node of a first node is decoded without waiting for a decoding of a second occupancy code for a second node having a same node size as the first node. Then, the processing circuitry reconstructs the octree structure based on the decoded occupancy codes for the nodes, and reconstructs the point cloud based on the octree structure.

INCORPORATION BY REFERENCE

This application is a Continuation of U.S. patent application Ser. No.17/063,411, filed Oct. 5, 2020, which claims the benefit of priority toU.S. Provisional Application No. 62/942,549, “HYBRID CODING ORDER FORPOINT CLOUD CODING” filed on Dec. 2, 2019, wherein the entire contentand disclosure of each of which is incorporated by reference herein inits entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to pointcloud coding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Various technologies are developed to capture and represent the world,such as objects in the world, environments in the world, and the like in3-dimensional (3D) space. 3D representations of the world can enablemore immersive forms of interaction and communication. Point clouds canbe used as a 3D representation of the world. A point cloud is a set ofpoints in a 3D space, each with associated attributes, e.g. color,material properties, texture information, intensity attributes,reflectivity attributes, motion related attributes, modality attributes,and various other attributes. Such point clouds may include largeamounts of data and may be costly and time-consuming to store andtransmit.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for pointcloud compression and decompression. In some examples, an apparatus forpoint cloud compression/decompression includes processing circuitry. Insome embodiments, the processing circuitry receives, from a codedbitstream for a point cloud, encoded occupancy codes for nodes in anoctree structure for the point cloud. The nodes in the octree structurecorrespond to three dimensional (3D) partitions of a space of the pointcloud. Sizes of the nodes are associated with sizes of the corresponding3D partitions. Further, the processing circuitry decodes, from theencoded occupancy codes, occupancy codes for the nodes. At least a firstoccupancy code for a child node of a first node is decoded withoutwaiting for a decoding of a second occupancy code for a second nodehaving a same node size as the first node. Then, the processingcircuitry reconstructs the octree structure based on the decodedoccupancy codes for the nodes, and reconstructs the point cloud based onthe octree structure.

In some embodiments, the processing circuitry decodes a first set ofoccupancy codes for a first set of nodes in a first sub octree with thefirst node being a root of the first sub octree and decodes a second setof occupancy codes for a second set of nodes in a second sub octree withthe second node being a root of the second sub octree. In an embodiment,the processing circuitry decodes the first set of occupancy codes forthe first set of nodes in the first sub octree in parallel with thesecond set of occupancy codes for the second set of nodes in the secondsub octree.

In another embodiment, the processing circuitry decodes, using a firstcoding mode, the first set of occupancy codes for the first set of nodesin the first sub octree and decodes, using a second coding mode, secondset of occupancy codes for the second set of nodes in the second suboctree. In an example, the processing circuitry decodes, from the codedbitstream, a first index that is indicative of the first coding mode forthe first sub octree, and decodes, from the coded bitstream, a secondindex that is indicative of the second coding mode for the second suboctree.

In some embodiments, the processing circuitry decodes a first portion ofoccupancy codes for larger nodes in the nodes using a first codingorder. The larger nodes are larger than a specific node size for codingorder change. The processing circuitry decodes a second portion ofoccupancy codes for smaller nodes in the nodes using a second codingorder that is different from the first coding order. The smaller nodesare equal or smaller than the specific node size for coding orderchange. In an example, the first coding order is breadth first codingorder and the second coding order is depth first coding order. Inanother example, the first coding order is depth first coding order andthe second coding order is breadth first coding order.

In some examples, the processing circuitry determines the specific nodesize for coding order change based on a signal in the coded bitstreamfor the point cloud. In an example, the processing circuitry decodes acontrol signal from the coded bitstream for the point cloud, and thecontrol signal is indicative of a change of coding order. Then, theprocessing circuitry decodes the signal and determines the specific nodesize for coding order change.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for point cloud encoding/decoding cause the computer to performany one or a combination of the methods for point cloudencoding/decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment;

FIG. 2 is a schematic illustration of a simplified block diagram of astreaming system in accordance with an embodiment;

FIG. 3 shows a block diagram of an encoder for encoding point cloudframes, according to some embodiments;

FIG. 4 shows a block diagram of a decoder for decoding a compressedbitstream corresponding to point cloud frames according to someembodiments;

FIG. 5 is a schematic illustration of a simplified block diagram of avideo decoder in accordance with an embodiment;

FIG. 6 is a schematic illustration of a simplified block diagram of avideo encoder in accordance with an embodiment;

FIG. 7 shows a block diagram of an encoder for encoding point cloudframes, according to some embodiments;

FIG. 8 shows a block diagram of a decoder for decoding a compressedbitstream corresponding to point cloud frames according to someembodiments;

FIG. 9 shows a diagram illustrating a partition of a cube based on theoctree partition technique according to some embodiments of thedisclosure.

FIG. 10 shows an example of an octree partition and an octree structurecorresponding to the octree partition according to some embodiments ofthe disclosure.

FIG. 11 shows a diagram of an octree structure illustrating breadthfirst coding order.

FIG. 12 shows a diagram of an octree structure illustrating depth firstcoding order.

FIG. 13 shows a syntax example of geometry parameter set according tosome embodiments of the disclosure.

FIG. 14 shows another syntax example of geometry parameter set accordingto some embodiments of the disclosure.

FIG. 15 shows a pseudo code example for octree coding according to someembodiments of the disclosure.

FIG. 16 shows a pseudo code example for depth first coding orderaccording to some embodiments of the disclosure.

FIG. 17 shows a flow chart outlining a process example in accordancewith some embodiments.

FIG. 18 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Aspects of the disclosure provide point cloud coding (PCC) techniques.PCC can be performed according to various schemes, such as ageometry-based scheme that is referred to as G-PCC, a video coding basedscheme that is referred to as V-PCC, and the like. According to someaspects of the disclosure, the G-PCC encodes the 3D geometry directlyand is a purely geometry-based approach without much to share with videocoding, and the V-PCC is heavily based on video coding. For example,V-PCC can map a point of the 3D cloud to a pixel of a 2D grid (animage). The V-PCC scheme can utilize generic video codecs for pointcloud compression. Moving picture experts group (MPEG) is working onG-PCC standard and V-PCC standard that respectively using the G-PCCscheme and the V-PCC scheme.

Aspects of the disclosure provide techniques for a hybrid coding orderthat can be used in PCC, such as the G-PCC scheme and the V-PCC scheme.The hybrid coding coder can include the depth first traverse scheme andbreadth first traverse scheme in a coding order. The present disclosurealso provides techniques for signaling the coding order.

Point Clouds can be widely used in many applications. For example, pointclouds can be used in autonomous driving vehicles for object detectionand localization; point clouds can be used in geographic informationsystems (GIS) for mapping, and can be used in cultural heritage tovisualize and archive cultural heritage objects and collections, etc.

Hereinafter, a point cloud generally may refer to a set of points in a3D space, each with associated attributes, e.g. color, materialproperties, texture information, intensity attributes, reflectivityattributes, motion related attributes, modality attributes, and variousother attributes. Point clouds can be used to reconstruct an object or ascene as a composition of such points. The points can be captured usingmultiple cameras, depth sensors or Lidar in various setups and may bemade up of thousands up to billions of points in order to realisticallyrepresent reconstructed scenes. A patch generally may refer to acontiguous subset of the surface described by the point cloud. In anexample, a patch includes points with surface normal vectors thatdeviate from one another less than a threshold amount.

Compression technologies can reduce the amount of data required torepresent a point cloud for faster transmission or reduction of storage.As such, technologies are needed for lossy compression of point cloudsfor use in real-time communications and six Degrees of Freedom (6 DoF)virtual reality. In addition, technology is sought for lossless pointcloud compression in the context of dynamic mapping for autonomousdriving and cultural heritage applications, and the like.

According to an aspect of the disclosure, the main philosophy behindV-PCC is to leverage existing video codecs to compress the geometry,occupancy, and texture of a dynamic point cloud as three separate videosequences. The extra metadata needed to interpret the three videosequences are compressed separately. A small portion of the overallbitstream is the metadata, which could be encoded/decoded efficientlyusing software implementation. The bulk of the information is handled bythe video codec.

FIG. 1 illustrates a simplified block diagram of a communication system(100) according to an embodiment of the present disclosure. Thecommunication system (100) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (150). Forexample, the communication system (100) includes a pair of terminaldevices (110) and (120) interconnected via the network (150). In theFIG. 1 example, the first pair of terminal devices (110) and (120) mayperform unidirectional transmission of point cloud data. For example,the terminal device (110) may compress a point cloud (e.g., pointsrepresenting a structure) that is captured by a sensor (105) connectedwith the terminal device (110). The compressed point cloud can betransmitted, for example in the form of a bitstream, to the otherterminal device (120) via the network (150). The terminal device (120)may receive the compressed point cloud from the network (150),decompress the bitstream to reconstruct the point cloud, and suitablydisplay the reconstructed point cloud. Unidirectional data transmissionmay be common in media serving applications and the like.

In the FIG. 1 example, the terminal devices (110) and (120) may beillustrated as servers, and personal computers, but the principles ofthe present disclosure may be not so limited. Embodiments of the presentdisclosure find application with laptop computers, tablet computers,smart phones, gaming terminals, media players, and/or dedicatedthree-dimensional (3D) equipment. The network (150) represents anynumber of networks that transmit compressed point cloud between theterminal devices (110) and (120). The network (150) can include forexample wireline (wired) and/or wireless communication networks. Thenetwork (150) may exchange data in circuit-switched and/orpacket-switched channels. Representative networks includetelecommunications networks, local area networks, wide area networks,and/or the Internet. For the purposes of the present discussion, thearchitecture and topology of the network (150) may be immaterial to theoperation of the present disclosure unless explained herein below.

FIG. 2 illustrates a simplified block diagram of a streaming system(200) in accordance with an embodiment. The FIG. 2 example is anapplication for the disclosed subject matter for a point cloud. Thedisclosed subject matter can be equally applicable to other point cloudenabled applications, such as, 3D telepresence application, virtualreality application, and the like.

The streaming system (200) may include a capture subsystem (213). Thecapture subsystem (213) can include a point cloud source (201), forexample light detection and ranging (LIDAR) systems, 3D cameras, 3Dscanners, a graphics generation component that generates theuncompressed point cloud in software, and the like that generates forexample point clouds (202) that are uncompressed. In an example, thepoint clouds (202) include points that are captured by the 3D cameras.The point clouds (202), depicted as a bold line to emphasize a high datavolume when compared to compressed point clouds (204) (a bitstream ofcompressed point clouds). The compressed point clouds (204) can begenerated by an electronic device (220) that includes an encoder (203)coupled to the point cloud source (201). The encoder (203) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The compressed point clouds (204) (or bitstream of compressedpoint clouds (204)), depicted as a thin line to emphasize the lower datavolume when compared to the stream of point clouds (202), can be storedon a streaming server (205) for future use. One or more streaming clientsubsystems, such as client subsystems (206) and (208) in FIG. 2 canaccess the streaming server (205) to retrieve copies (207) and (209) ofthe compressed point cloud (204). A client subsystem (206) can include adecoder (210), for example, in an electronic device (230). The decoder(210) decodes the incoming copy (207) of the compressed point clouds andcreates an outgoing stream of reconstructed point clouds (211) that canbe rendered on a rendering device (212).

It is noted that the electronic devices (220) and (230) can includeother components (not shown). For example, the electronic device (220)can include a decoder (not shown) and the electronic device (230) caninclude an encoder (not shown) as well.

In some streaming systems, the compressed point clouds (204), (207), and(209) (e.g., bitstreams of compressed point clouds) can be compressedaccording to certain standards. In some examples, video coding standardsare used in the compression of point clouds. Examples of those standardsinclude, High Efficiency Video Coding (HEVC), Versatile Video Coding(VVC), and the like.

FIG. 3 shows a block diagram of a V-PCC encoder (300) for encoding pointcloud frames, according to some embodiments. In some embodiments, theV-PCC encoder (300) can be used in the communication system (100) andstreaming system (200). For example, the encoder (203) can be configuredand operate in a similar manner as the V-PCC encoder (300).

The V-PCC encoder (300) receives point cloud frames as uncompressedinputs and generates bitstream corresponding to compressed point cloudframes. In some embodiments, the V-PCC encoder (300) may receive thepoint cloud frames from a point cloud source, such as the point cloudsource (201) and the like.

In the FIG. 3 example, the V-PCC encoder (300) includes a patchgeneration module (306), a patch packing module (308), a geometry imagegeneration module (310), a texture image generation module (312), apatch info module (304), an occupancy map module (314), a smoothingmodule (336), image padding modules (316) and (318), a group dilationmodule (320), video compression modules (322), (323) and (332), anauxiliary patch info compression module (338), an entropy compressionmodule (334), and a multiplexer (324).

According to an aspect of the disclosure, the V-PCC encoder (300),converts 3D point cloud frames into an image-based representation alongwith some meta data (e.g., occupancy map and patch info) that is used toconvert the compressed point cloud back into a decompressed point cloud.In some examples, the V-PCC encoder (300) can convert 3D point cloudframes into geometry images, texture images and occupancy maps, and thenuse video coding techniques to encode the geometry images, textureimages and occupancy maps into a bitstream. Generally, a geometry imageis a 2D image with pixels filled with geometry values associated withpoints projected to the pixels, and a pixel filled with a geometry valuecan be referred to as a geometry sample. A texture image is a 2D imagewith pixels filled with texture values associated with points projectedto the pixels, and a pixel filled with a texture value can be referredto as a texture sample. An occupancy map is a 2D image with pixelsfilled with values that indicate occupied or unoccupied by patches.

The patch generation module (306) segments a point cloud into a set ofpatches (e.g., a patch is defined as a contiguous subset of the surfacedescribed by the point cloud), which may be overlapping or not, suchthat each patch may be described by a depth field with respect to aplane in 2D space. In some embodiments, the patch generation module(306) aims at decomposing the point cloud into a minimum number ofpatches with smooth boundaries, while also minimizing the reconstructionerror.

The patch info module (304) can collect the patch information thatindicates sizes and shapes of the patches. In some examples, the patchinformation can be packed into an image frame and then encoded by theauxiliary patch info compression module (338) to generate the compressedauxiliary patch information.

The patch packing module (308) is configured to map the extractedpatches onto a 2 dimensional (2D) grid while minimize the unused spaceand guarantee that every M×M (e.g., 16×16) block of the grid isassociated with a unique patch. Efficient patch packing can directlyimpact the compression efficiency either by minimizing the unused spaceor ensuring temporal consistency.

The geometry image generation module (310) can generate 2D geometryimages associated with geometry of the point cloud at given patchlocations. The texture image generation module (312) can generate 2Dtexture images associated with texture of the point cloud at given patchlocations. The geometry image generation module (310) and the textureimage generation module (312) exploit the 3D to 2D mapping computedduring the packing process to store the geometry and texture of thepoint cloud as images. In order to better handle the case of multiplepoints being projected to the same sample, each patch is projected ontotwo images, referred to as layers. In an example, geometry image isrepresented by a monochromatic frame of W×H in YUV420-8 bit format. Togenerate the texture image, the texture generation procedure exploitsthe reconstructed/smoothed geometry in order to compute the colors to beassociated with the re-sampled points.

The occupancy map module (314) can generate an occupancy map thatdescribes padding information at each unit. For example, the occupancyimage includes a binary map that indicates for each cell of the gridwhether the cell belongs to the empty space or to the point cloud. In anexample, the occupancy map uses binary information describing for eachpixel whether the pixel is padded or not. In another example, theoccupancy map uses binary information describing for each block ofpixels whether the block of pixels is padded or not.

The occupancy map generated by the occupancy map module (314) can becompressed using lossless coding or lossy coding. When lossless codingis used, the entropy compression module (334) is used to compress theoccupancy map. When lossy coding is used, the video compression module(332) is used to compress the occupancy map.

It is noted that the patch packing module (308) may leave some emptyspaces between 2D patches packed in an image frame. The image paddingmodules (316) and (318) can fill the empty spaces (referred to aspadding) in order to generate an image frame that may be suited for 2Dvideo and image codecs. The image padding is also referred to asbackground filling which can fill the unused space with redundantinformation. In some examples, a good background filling minimallyincreases the bit rate while does not introduce significant codingdistortion around the patch boundaries.

The video compression modules (322), (323), and (332) can encode the 2Dimages, such as the padded geometry images, padded texture images, andoccupancy maps based on a suitable video coding standard, such as HEVC,VVC and the like. In an example, the video compression modules (322),(323), and (332) are individual components that operate separately. Itis noted that the video compression modules (322), (323), and (332) canbe implemented as a single component in another example.

In some examples, the smoothing module (336) is configured to generate asmoothed image of the reconstructed geometry image. The smoothed imagecan be provided to the texture image generation (312). Then, the textureimage generation (312) may adjust the generation of the texture imagebased on the reconstructed geometry images. For example, when a patchshape (e.g. geometry) is slightly distorted during encoding anddecoding, the distortion may be taken into account when generating thetexture images to correct for the distortion in patch shape.

In some embodiments, the group dilation (320) is configured to padpixels around the object boundaries with redundant low-frequency contentin order to improve coding gain as well as visual quality ofreconstructed point cloud.

The multiplexer (324) can multiplex the compressed geometry image, thecompressed texture image, the compressed occupancy map, the compressedauxiliary patch information into a compressed bitstream.

FIG. 4 shows a block diagram of a V-PCC decoder (400) for decodingcompressed bitstream corresponding to point cloud frames, according tosome embodiments. In some embodiments, the V-PCC decoder (400) can beused in the communication system (100) and streaming system (200). Forexample, the decoder (210) can be configured to operate in a similarmanner as the V-PCC decoder (400). The V-PCC decoder (400) receives thecompressed bitstream, and generates reconstructed point cloud based onthe compressed bitstream.

In the FIG. 4 example, the V-PCC decoder (400) includes a de-multiplexer(432), video decompression modules (434) and (436), an occupancy mapdecompression module (438), an auxiliary patch-information decompressionmodule (442), a geometry reconstruction module (444), a smoothing module(446), a texture reconstruction module (448), and a color smoothingmodule (452).

The de-multiplexer (432) can receive and separate the compressedbitstream into compressed texture image, compressed geometry image,compressed occupancy map, and compressed auxiliary patch information.

The video decompression modules (434) and (436) can decode thecompressed images according to a suitable standard (e.g., HEVC, VVC,etc.) and output decompressed images. For example, the videodecompression module (434) decodes the compressed texture images andoutputs decompressed texture images; and the video decompression module(436) decodes the compressed geometry images and outputs thedecompressed geometry images.

The occupancy map decompression module (438) can decode the compressedoccupancy maps according to a suitable standard (e.g., HEVC, VVC, etc.)and output decompressed occupancy maps.

The auxiliary patch-information decompression module (442) can decodethe compressed auxiliary patch information according to a suitablestandard (e.g., HEVC, VVC, etc.) and output decompressed auxiliary patchinformation.

The geometry reconstruction module (444) can receive the decompressedgeometry images, and generate reconstructed point cloud geometry basedon the decompressed occupancy map and decompressed auxiliary patchinformation.

The smoothing module (446) can smooth incongruences at edges of patches.The smoothing procedure aims at alleviating potential discontinuitiesthat may arise at the patch boundaries due to compression artifacts. Insome embodiments, a smoothing filter may be applied to the pixelslocated on the patch boundaries to alleviate the distortions that may becaused by the compression/decompression.

The texture reconstruction module (448) can determine textureinformation for points in the point cloud based on the decompressedtexture images and the smoothing geometry.

The color smoothing module (452) can smooth incongruences of coloring.Non-neighboring patches in 3D space are often packed next to each otherin 2D videos. In some examples, pixel values from non-neighboringpatches might be mixed up by the block-based video codec. The goal ofcolor smoothing is to reduce the visible artifacts that appear at patchboundaries.

FIG. 5 shows a block diagram of a video decoder (510) according to anembodiment of the present disclosure. The video decoder (510) can beused in the V-PCC decoder (400). For example, the video decompressionmodules (434) and (436), the occupancy map decompression module (438)can be similarly configured as the video decoder (510).

The video decoder (510) may include a parser (520) to reconstructsymbols (521) from compressed images, such as the coded video sequence.Categories of those symbols include information used to manage operationof the video decoder (510). The parser (520) may parse/entropy-decodethe coded video sequence that is received. The coding of the coded videosequence can be in accordance with a video coding technology orstandard, and can follow various principles, including variable lengthcoding, Huffman coding, arithmetic coding with or without contextsensitivity, and so forth. The parser (520) may extract from the codedvideo sequence, a set of subgroup parameters for at least one of thesubgroups of pixels in the video decoder, based upon at least oneparameter corresponding to the group. Subgroups can include Groups ofPictures (GOPs), pictures, tiles, slices, macroblocks, Coding Units(CUs), blocks, Transform Units (TUs), Prediction Units (PUs) and soforth. The parser (520) may also extract from the coded video sequenceinformation such as transform coefficients, quantizer parameter values,motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from a buffer memory, so as to createsymbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (520). The flow of such subgroup control information between theparser (520) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values that canbe input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (558). The currentpicture buffer (558) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(555), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (552) has generated to the outputsample information as provided by the scaler/inverse transform unit(551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to a render device as well as stored in the reference picturememory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

FIG. 6 shows a block diagram of a video encoder (603) according to anembodiment of the present disclosure. The video encoder (603) can beused in the V-PCC encoder (300) the compresses point clouds. In anexample, the video compression module (322) and (323), and the videocompression module (332) are configured similarly to the encoder (603).

The video encoder (603) may receive images, such as padded geometryimages, padded texture images and the like, and generate compressedimages.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence (images) into a codedvideo sequence (compressed images) in real time or under any other timeconstraints as required by the application. Enforcing appropriate codingspeed is one function of a controller (650). In some embodiments, thecontroller (650) controls other functional units as described below andis functionally coupled to the other functional units. The coupling isnot depicted for clarity. Parameters set by the controller (650) caninclude rate control related parameters (picture skip, quantizer, lambdavalue of rate-distortion optimization techniques, . . . ), picture size,group of pictures (GOP) layout, maximum motion vector search range, andso forth. The controller (650) can be configured to have other suitablefunctions that pertain to the video encoder (603) optimized for acertain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (634). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (634) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5 . Brieflyreferring also to FIG. 5 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including and parser (520) may not befully implemented in the local decoder (633).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

A video may be in the form of a plurality of source pictures (images) ina temporal sequence. Intra-picture prediction (often abbreviated tointra prediction) makes use of spatial correlation in a given picture,and inter-picture prediction makes uses of the (temporal or other)correlation between the pictures. In an example, a specific pictureunder encoding/decoding, which is referred to as a current picture, ispartitioned into blocks. When a block in the current picture is similarto a reference block in a previously coded and still buffered referencepicture in the video, the block in the current picture can be coded by avector that is referred to as a motion vector. The motion vector pointsto the reference block in the reference picture, and can have a thirddimension identifying the reference picture, in case multiple referencepictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 7 shows a block diagram of a G-PPC encoder (700) in accordance withan embodiment. The encoder (700) can be configured to receive pointcloud data and compress the point cloud data to generate a bit streamcarrying compressed point cloud data. In an embodiment, the encoder(700) can include a position quantization module (710), a duplicatedpoints removal module (712), an octree encoding module (730), anattribute transfer module (720), a level of detail (LOD) generationmodule (740), an attribute prediction module (750), a residualquantization module (760), an arithmetic coding module (770), an inverseresidual quantization module (780), an addition module (781), and amemory (790) to store reconstructed attribute values.

As shown, an input point cloud (701) can be received at the encoder(700). Positions (e.g., 3D coordinates) of the point cloud (701) areprovided to the quantization module (710). The quantization module (710)is configured to quantize the coordinates to generate quantizedpositions. The duplicated points removal module (712) is configured toreceive the quantized positions and perform a filter process to identifyand remove duplicated points. The octree encoding module (730) isconfigured to receive filtered positions from the duplicated pointsremoval module (712), and perform an octree-based encoding process togenerate a sequence of occupancy codes that describe a 3D grid ofvoxels. The occupancy codes are provided to the arithmetic coding module(770).

The attribute transfer module (720) is configured to receive attributesof the input point cloud, and perform an attribute transfer process todetermine an attribute value for each voxel when multiple attributevalues are associated with the respective voxel. The attribute transferprocess can be performed on the re-ordered points output from the octreeencoding module (730). The attributes after the transfer operations areprovided to the attribute prediction module (750). The LOD generationmodule (740) is configured to operate on the re-ordered points outputfrom the octree encoding module (730), and re-organize the points intodifferent LODs. LOD information is supplied to the attribute predictionmodule (750).

The attribute prediction module (750) processes the points according toan LOD-based order indicated by the LOD information from the LODgeneration module (740). The attribute prediction module (750) generatesan attribute prediction for a current point based on reconstructedattributes of a set of neighboring points of the current point stored inthe memory (790). Prediction residuals can subsequently be obtainedbased on original attribute values received from the attribute transfermodule (720) and locally generated attribute predictions. When candidateindices are used in the respective attribute prediction process, anindex corresponding to a selected prediction candidate may be providedto the arithmetic coding module (770).

The residual quantization module (760) is configured to receive theprediction residuals from the attribute prediction module (750), andperform quantization to generate quantized residuals. The quantizedresiduals are provided to the arithmetic coding module (770).

The inverse residual quantization module (780) is configured to receivethe quantized residuals from the residual quantization module (760), andgenerate reconstructed prediction residuals by performing an inverse ofthe quantization operations performed at the residual quantizationmodule (760). The addition module (781) is configured to receive thereconstructed prediction residuals from the inverse residualquantization module (780), and the respective attribute predictions fromthe attribute prediction module (750). By combining the reconstructedprediction residuals and the attribute predictions, the reconstructedattribute values are generated and stored to the memory (790).

The arithmetic coding module (770) is configured to receive theoccupancy codes, the candidate indices (if used), the quantizedresiduals (if generated), and other information, and perform entropyencoding to further compress the received values or information. As aresult, a compressed bitstream (702) carrying the compressed informationcan be generated. The bitstream (702) may be transmitted, or otherwiseprovided, to a decoder that decodes the compressed bitstream, or may bestored in a storage device.

FIG. 8 shows a block diagram of a G-PCC decoder (800) in accordance withan embodiment. The decoder (800) can be configured to receive acompressed bitstream and perform point cloud data decompression todecompress the bitstream to generate decoded point cloud data. In anembodiment, the decoder (800) can include an arithmetic decoding module(810), an inverse residual quantization module (820), an octree decodingmodule (830), an LOD generation module (840), an attribute predictionmodule (850), and a memory (860) to store reconstructed attributevalues.

As shown, a compressed bitstream (801) can be received at the arithmeticdecoding module (810). The arithmetic decoding module (810) isconfigured to decode the compressed bitstream (801) to obtain quantizedresiduals (if generated) and occupancy codes of a point cloud. Theoctree decoding module (830) is configured to determine reconstructedpositions of points in the point cloud according to the occupancy codes.The LOD generation module (840) is configured to re-organize the pointsinto different LODs based on the reconstructed positions, and determinean LOD-based order. The inverse residual quantization module (820) isconfigured to generate reconstructed residuals based on the quantizedresiduals received from the arithmetic decoding module (810).

The attribute prediction module (850) is configured to perform anattribute prediction process to determine attribute predictions for thepoints according to the LOD-based order. For example, an attributeprediction of a current point can be determined based on reconstructedattribute values of neighboring points of the current point stored inthe memory (860). The attribute prediction module (850) can combine theattribute prediction with a respective reconstructed residual togenerate a reconstructed attribute for the current point.

A sequence of reconstructed attributes generated from the attributeprediction module (850) together with the reconstructed positionsgenerated from the octree decoding module (830) corresponds to a decodedpoint cloud (802) that is output from the decoder (800) in one example.In addition, the reconstructed attributes are also stored into thememory (860) and can be subsequently used for deriving attributepredictions for subsequent points.

In various embodiments, the encoder (300), the decoder (400), theencoder (700), and/or the decoder (800) can be implemented withhardware, software, or combination thereof. For example, the encoder(300), the decoder (400), the encoder (700), and/or the decoder (800)can be implemented with processing circuitry such as one or moreintegrated circuits (ICs) that operate with or without software, such asan application specific integrated circuit (ASIC), field programmablegate array (FPGA), and the like. In another example, the encoder (300),the decoder (400), the encoder (700), and/or the decoder (800) can beimplemented as software or firmware including instructions stored in anon-volatile (or non-transitory) computer-readable storage medium. Theinstructions, when executed by processing circuitry, such as one or moreprocessors, causing the processing circuitry to perform functions of theencoder (300), the decoder (400), the encoder (700), and/or the decoder(800).

It is noted that the attribute prediction modules (750) and (850)configured to implement the attribute prediction techniques disclosedherein can be included in other decoders or encoders that may havesimilar or different structures from what is shown in FIG. 7 and FIG. 8. In addition, the encoder (700) and decoder (800) can be included in asame device, or separate devices in various examples.

According to some aspects of the disclosure, geometry octree structurecan be used in PCC. In some related examples, the geometry octreestructure is traversed in a breadth first order. According to thebreadth first order, octree nodes in a current level can be visitedafter the octree nodes in an upper level have been visited. According toan aspect of the present disclosure, the breadth first order scheme isnot suitable for parallel processing because the current level has towait for the upper level to be coded. The present disclosure providestechniques to add depth first coding order in the coding ordertechniques for geometry octree structure. The depth first coding ordercan be combined with the breadth first order in some embodiments, or canbe used by itself in some embodiments. The coding orders (e.g., depthfirst coding order, a combination of the depth first coding order andthe breadth first coding order and the like) can be referred to ashybrid coding order for PCC in the present disclosure.

The proposed methods may be used separately or combined in any order.Further, each of the methods (or embodiments), encoder, and decoder maybe implemented by processing circuitry (e.g., one or more processors orone or more integrated circuits). In one example, the one or moreprocessors execute a program that is stored in a non-transitorycomputer-readable medium.

According to some aspects of the disclosure, geometry information andthe associated attributes of a point cloud, such as color, reflectanceand the like can be separately compressed (e.g., in the Test Model 13(TMC13) model). The geometry information of the point cloud, whichincludes the 3D coordinates of the points in the point cloud, can becoded by an octree partition with occupancy information of thepartitions. The attributes can be compressed based on a reconstructedgeometry using, for example, prediction, lifting and region adaptivehierarchical transform techniques.

According to some aspects of the disclosure, a three dimensional spacecan be partitioned using octree partition. Octrees are the threedimensional analog of quadtrees in the two dimensional space. Octreepartition technique refers to the partition technique that recursivelysubdivides three dimensional space into eight octants, and an octreestructure refers to the tree structure that represents the partitions.In an example, each node in the octree structure corresponds to a threedimensional space, and the node can be an end node (no more partition,also referred to as leaf node in some examples) or a node with a furtherpartition. A partition at a node can partition the three dimensionalspace represented by the node into eight octants. In some examples,nodes corresponding to partitions of a specific node can be referred toas child nodes of the specific node.

FIG. 9 shows a diagram illustrating a partition of a 3D cube (900)(corresponding to a node) based on the octree partition techniqueaccording to some embodiments of the disclosure. The partition candivide the 3D cube (900) into eight smaller equal-sized cubes 0-7 asshown in FIG. 9 .

The octree partition technique (e.g., in TMC13) can recursively dividean original 3D space into the smaller units, and the occupancyinformation of every sub-space can be encoded to represent geometrypositions.

In some embodiments (e.g., In TMC13), an octree geometry codec is used.The octree geometry codec can perform geometry encoding. In someexamples, geometry encoding is performed on a cubical box. For example,the cubical box can be an axis-aligned bounding box B that is defined bytwo points (0,0,0) and (2^(M-1), 2^(M-1), 2′^(M-1)), where 2^(M-1)defines the size of the bounding box B and M can be specified in thebitstream.

Then, an octree structure is built by recursively subdividing thecubical box. For example, the cubical box defined by the two points(0,0,0) and (2′^(M-1), 2^(M-1), 2^(M-1)) is divided into 8 sub cubicalboxes, then an 8-bit code, that is referred to as an occupancy code, isgenerated. Each bit of the occupancy code is associated with a subcubical box, and the value of the bit is used to indicate whether theassociated sub cubical box contains any points of the point cloud. Forexample, value 1 of a bit indicates that the sub cubical box associatedwith the bit contains one or more points of the point cloud; and value 0of a bit indicates that the sub cubical box associated with the bitcontains no point of the point cloud.

Further, for empty sub cubical box (e.g., the value of the bitassociated with the sub cubical box is 0), no more division is appliedon the sub cubical box. When a sub cubical box has one or more points ofthe point cloud (e.g., the value of the bit associated with the subcubical box is 1), the sub cubical box is further divided into 8 smallersub cubical boxes, and an occupancy code can be generated for the subcubical box to indicate the occupancy of the smaller sub cubical boxes.In some examples, the subdivision operations can be repetitivelyperformed on non-empty sub cubical boxes until the size of the subcubical boxes is equal to a predetermined threshold, such as sizebeing 1. In some examples, the sub cubical boxes with a size of 1 arereferred to as voxels, and the sub cubical boxes that have larger sizesthan voxels can be referred to as non-voxels.

FIG. 10 shows an example of an octree partition (1010) and an octreestructure (1020) corresponding to the octree partition (1010) accordingto some embodiments of the disclosure. FIG. 10 shows two levels ofpartitions in the octree partition (1010). The octree structure (1020)includes a node (NO) corresponding to the cubical box for octreepartition (1010). At a first level, the cubical box is partitioned into8 sub cubical boxes that are numbered 0-7 according to the numberingtechnique shown in FIG. 9 . The occupancy code for the partition of thenode N0 is “10000001” in binary, which indicates the first sub cubicalbox represented by node N0-0 and the eighth sub cubical box representedby node N0-7 includes points in the point cloud and other sub cubicalboxes are empty.

Then, at the second level of partition, the first sub cubical box(represented by node N0-0) and the eighth sub cubical box (representedby node N0-7) are further respectively sub-divided into eight octants.For example, the first sub cubical box (represented by node NO-0) ispartitioned into 8 smaller sub cubical boxes that are numbered 0-7according to the numbering technique shown in FIG. 9 . The occupancycode for the partition of the node N0-0 is “00011000” in binary, whichindicates the fourth smaller sub cubical box (represented by nodeN0-0-3) and the fifth smaller sub cubical box (represented by nodeN0-0-4) includes points in the point cloud and other smaller sub cubicalboxes are empty. At the second level, the seventh sub cubical box(represented by node N0-7) is similarly partitioned into 8 smaller subcubical boxes as shown in FIG. 10 .

In the FIG. 10 example, the nodes corresponding to non-empty cubicalspace (e.g., cubical box, sub cubical boxes, smaller sub cubical boxesand the like) are colored in grey, and referred to as shaded nodes.

According to some aspects of the disclosure, the occupancy codes can besuitably compressed using suitable coding techniques. In someembodiments, an arithmetic encoder is used to compress an occupancy codeof a current node in the octree structure. The occupancy code can bedenoted as S which is an 8-bit integer, and each bit in S indicates anoccupancy status of a child node of the current node. In an embodiment,the occupancy code is encoded using a bit wise encoding. In anotherembodiment, the occupancy code is encoded using a byte wise encoding. Insome examples (e.g., TMC13), the bit-wise encoding is enabled bydefault. Both of the bit wise encoding and the byte wise encoding canperform arithmetic coding with context modeling to encode the occupancycode. The context status can be initialized at the beginning of thewhole coding process for the occupancy codes and is updated during thecoding process of the occupancy codes.

In an embodiment of bit-wise encoding to encode an occupancy code for acurrent node, eight bins in S for the current node are encoded in acertain order. Each bin in S is encoded by referring to the occupancystatus of neighboring nodes of the current code and/or child nodes ofthe neighboring nodes. The neighboring nodes are at the same level asthe current node, and can be referred to as sibling nodes of the currentnode.

In an embodiment of byte wise encoding to encode an occupancy code for acurrent node, the occupancy code S (one byte) can be encoded byreferring to: (1) an adaptive look up table (A-LUT), which keeps trackof the P (e.g., 32) most frequent used occupancy codes; and (2) a cachewhich keeps track of the last different observed Q (e.g., 16) occupancycodes.

In some examples for byte wise encoding, a binary flag indicatingwhether S is in the A-LUT or not is encoded. If S is in the A-LUT, theindex in the A-LUT is encoded by using a binary arithmetic encoder. If Sis not in the A-LUT, then a binary flag indicating whether S is in thecache or not is encoded. If S is in the cache, then the binaryrepresentation of its index in the cache is encoded by using a binaryarithmetic encoder. Otherwise, if S is not in the cache, then the binaryrepresentation of S is encoded by using a binary arithmetic encoder.

In some embodiments, at a decoder side, a decoding process can start byparsing the dimensions of a bounding box from the bitstream. Thebounding box is indicative of the cubical box corresponding to a rootnode in the octree structure for partitioning the cubical box accordingto geometry information of the point cloud (e.g., occupancy informationfor points in the point cloud). The octree structure is then built bysubdividing the cubical box according to the decoded occupancy codes.

In some related examples, (e.g., a version of TMC13), to code theoccupancy codes, the octree structure is traversed in the breadth firstorder. According to the breadth first order, octree nodes (nodes in theoctree structure) in a level can be visited after all of the octreenodes in an upper level have been visited. In an implementation example,a first-in-first-out (FIFO) data structure can be used.

FIG. 11 shows a diagram of an octree structure (1100) illustratingbreadth first coding order. The shaded nodes in the octree structure(1100) are nodes corresponding to cubical spaces that are not empty. Theoccupancy codes for the shaded nodes can be coded in the breadth firstcoding order from 0 to 8 shown in FIG. 11 . In the breadth first codingorder, the octree nodes are visited level-by-level. The breadth firstcoding order by itself is not suitable for parallel processing becausethe current level has to wait for the upper level to be coded.

Some aspects of the disclosure provide a hybrid coding order thatincludes at least one level that is coded using a depth first codingorder instead of the breadth first coding order. Thus, in someembodiments, a node at the level with the depth first coding order anddescendant nodes of the node can form a sub octree structure of theoctree structure. When the level with depth first coding order includesmultiple nodes respectively corresponding to non-empty cubical spaces,the multiple nodes and their corresponding descendant nodes can formmultiple sub octree structures. The multiple sub octree structures canbe coded in parallel in some embodiments.

FIG. 12 shows a diagram of an octree structure (1200) illustrating depthfirst coding order. The shaded nodes in the octree structure (1200) arenodes corresponding to cubical spaces that are not empty. The octreestructure (1200) can correspond to same occupancy geometry of a pointcloud as the octree structure (1100). The occupancy codes for the shadednodes can be coded in the depth first coding order from 0 to 8 shown inFIG. 12 .

In the FIG. 12 example, node “0” can be at any suitable partition depth,such as PD0, child nodes of the node “0” are at the partition depthPD0+1, and grandchild nodes of the node “0” are at the partition depthPD0+2. In the FIG. 12 example, nodes at partition depth PD0+1 can becoded in a depth first coding order. The nodes at the partition depthPD0+1 include two nodes that correspond to non-empty space. The twonodes and their respectively descendant nodes can form a first suboctree structure (1210) and a second sub octree structure (1220), thetwo nodes can be respectively referred to as root nodes of the two suboctree structures.

The depth first coding order in FIG. 12 is referred to as a preorderversion of the depth first coding order. In the preorder version of thedepth first coding order, for each sub octree structure, the root nodeof the sub octree is visited first before visiting the child nodes ofthe sub octree structure. Further, the deepest node is first visited andthen track back to the siblings of the parent node.

In the FIG. 12 example, the first sub octree structure (1210) and thesecond sub octree structure (1220) can be coded in parallel processingin some implementations. For example, node 1 and node 5 can be visitedat the same time. In some examples, recursion programming or stack datastructure can be used to implement the depth first coding order.

In some embodiments, the hybrid coding order starts with the breadthfirst traversing (coding), and after several levels of breadth firsttraversing, the depth-first traversing (coding) can be enabled.

It should be noted that the hybrid coding order can be used in anysuitable PCC system, such as the TMC13 based PCC system, MPEG-PCC basedPCC system, and the like.

According to an aspect of the disclosure, the hybrid coding order caninclude both breadth first coding order and depth first coding order forcoding geometry information of a point cloud. In an embodiment, a nodesize for nodes in the octree structure to change from breadth firstcoding order to depth first coding order can be specified. In anexample, during PCC, the coding of the octree structure starts withbreadth first coding order, and at a level with node size being equal tothe specified node size for coding order change, the coding order canchange to the depth first coding order at the level. It is noted thatnode size is associated with partition depth in some examples.

In another embodiment, a node size for nodes in the octree structure tochange from depth first coding order to breadth first coding order canbe specified. In an example, during PCC, the coding of the octreestructure starts with depth first coding order, and at a level with nodesize being equal to the specified node size for coding order change, thecoding order can change to the breadth first coding order. It is notedthat node size is associated with partition depth in some examples.

More specifically, in the embodiment of starting with breadth firstcoding order, the node size can be represented in log 2 scale, and isdenoted by d=0, 1, . . . , M−1, where M−1 is the node size of the rootnode and M is the maximum number of octree partition depths (alsoreferred to as levels in some examples). Further, a parameter d_(t) thatis referred to as a coding order change size can be defined. In anexample, the parameter d_(t) (1≤d_(t)≤M−1), is used to specify that thebreadth-first order is applied to the nodes from the size of M−1 tod_(t) and the depth-first order is applied to the nodes from the size ofd_(t)−1 to 0. When d_(t)=M−1, the depth-first scheme applied to all theoctree nodes from the root node. When d_(t)=1, the octree structure iscoded using breadth first coding order only.

In some embodiments, the coding order for the octree structure can startwith breadth first coding order, then at a specific depth (correspondingto specific node size), each node at the specific depth and thedescendant nodes of the node form a separate sub octree structure of thepoint cloud. Thus, at the specific depth, multiple sub octree structuresare formed. The sub octree structures can be separately coded using anysuitable coding mode. In an example, a sub octree structure can be codedusing depth first coding order. In another example, a sub octreestructure can be coded using breadth first coding order. In anotherexample, a sub octree structure can be coded using a hybrid codingorder. In another example, occupancy codes in a sub octree structure canbe coded using bit wise coding scheme. In another example, occupancycodes in a sub octree structure can be coded using byte wise codingscheme. In another example, a sub octree structure can be coded usingpredictive geometry coding technique which is an alternative coding modeof depth-first octree coding mode. The predictive geometry codingtechnique can predict points based on previously coded neighboringpoints with coded corrective vectors in some examples.

In some embodiments, at the encoder side, for each sub octree structure,the encoder can select a coding mode from multiple coding modes based oncoding efficiencies. For example, a selected coding mode for a suboctree structure can achieve the best coding efficiency for the suboctree structure. Then, the encoder can use respectively selected codingmodes for the sub octree structures to respectively code the sub octreestructures. In some embodiments, the encoder can signal an index for asub octree structure in the bitstream and the index is indicative of theselected coding mode for the sub octree structure. At the decoder side,the decoder can determine the coding mode for a sub octree structurebased on the index in the bitstream and then decode sub octree structureaccording to the coding mode.

Aspects of the present disclosure also provide signaling techniques forthe hybrid coding order. According to an aspect of the disclosure,controlling parameters to be used in the hybrid coding order can besignaled in high level syntax, such as sequence parameter set (SPS),slice header, geometry parameter set of the bitstream, and the like. Itis noted that specific examples are provided in the followingdescription. The disclosed techniques illustrated by the specificexamples are not limited to the specific examples, and can be suitablyadjusted and used in other examples.

In an embodiment, the parameter d_(t) (the coding order change size) isspecified in the high-level syntax.

FIG. 13 shows a syntax example (1300) of geometry parameter setaccording to some embodiments of the disclosure. As shown by (1310),gps_depth_first_node_size_log 2_minus_1 is specified in the geometryparameter set. The parameter d_(t) can be determined based ongps_depth_first_node_size_log 2_minus_1, for example, according to (Eq.1).d _(t)=gps_depth_first_node_size_log 2_minus_1+1  (Eq. 1)

It is noted that when gps_depth_first_node_size_log 2_minus_1 equals to0, the depth first coding order is disabled.

In another embodiment, a control flag is explicitly signaled to indicatewhether hybrid coding order is used.

FIG. 14 shows another syntax example (1400) of geometry parameter setaccording to some embodiments of the disclosure. As shown by (1410), acontrol flag that is denoted by gps_hybrid_coding_order_flag is used.When the control flag gps_hybrid_coding_order_flag is true (e.g., hasvalue 1), the hybrid coding order scheme is enabled; whengps_hybrid_coding_order_flag is false (e.g., has value 0), the hybridcoding order scheme is disabled. When gps_hybrid_coding_order_flag istrue (e.g., has value 1), the parameter d_(t) can be determined based ongps_depth_first_node_size_log 2_minus_2, for example, according to (Eq.2):d _(t)=gps_depth_first_node_size_log 2_minus2+2  (Eq. 2)When gps_hybrid_coding_order_flag is false (e.g., has value 0), d_(t) isset to 1 by default to indicate the depth-first coding order is disabledand only the breadth-first coding order is applied in an example.

In an embodiment, when the hybrid coding order is enabled, thebreadth-first order is applied to the nodes from the size of M−1 tod_(t) and the depth-first order is applied to the nodes from the size ofd_(t)−1 to 0.

FIG. 15 shows a pseudo code example (1500) for octree coding accordingto some embodiments of the disclosure. As shown by (1510), whendepth>=MaxGeometryOctreeDepth−d_(t), depth first coding order can beused. In the FIG. 15 example, the pseudo code“geometry_node_depth_first” can be applied for depth first coding order.

FIG. 16 shows a pseudo code example (1600) for depth first coding orderaccording to some embodiments of the disclosure. The pseudo code“geometry_node_depth_first” is a recursive function. In the recursivefunction, “geometry_node” function is first invoked to obtain theoccupancy code for current octree node, and then the pseudo code“geometry_node_depth_first” is invoked by itself to code each child nodeuntil reaching the leaf nodes, for example, whendepth>=MaxGeometryOctreeDepth−1.

FIG. 17 shows a flow chart outlining a process (1700) according to anembodiment of the disclosure. The process (1700) can be used during acoding process for point clouds. In various embodiments, the process(1700) is executed by processing circuitry, such as the processingcircuitry in the terminal devices (110), the processing circuitry thatperforms functions of the encoder (203) and/or the decoder (201), theprocessing circuitry that performs functions of the encoder (300), thedecoder (400), the encoder (700), and/or the decoder (800), and thelike. In some embodiments, the process (1700) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (1700). Theprocess starts at (S1701) and proceeds to (S1710).

At (S1710), a coded bitstream for a point cloud is received. The codedbistream includes geometry information in the form of encoded occupancycodes for nodes in an octree structure for the point cloud. The nodes inthe octree structure correspond to three dimensional (3D) partitions ofa space of the point cloud. Sizes of the nodes are associated with sizesof the corresponding 3D partitions.

At (S1720), occupancy codes for the nodes are decoded from the encodedoccupancy codes. At least a first occupancy code for a child node of afirst node is decoded without waiting for a decoding of a secondoccupancy code for a second node having a same node size as the firstnode.

In an embodiment, the child node is among a first set of nodes (firstdescendant nodes) in a first sub octree with the first node being a rootof the first sub octree. The first node and the second node are siblingnodes of the same node size. The second node is the root node of asecond sub octree that includes a second set of nodes (second descendantnodes). Then, in some examples, a first set of occupancy codes for thefirst set of nodes and a second set of occupancy codes for the secondset of nodes can be decoded separately. In an example, the first set ofoccupancy codes for the first set of nodes and the second set ofoccupancy codes for the second set of nodes can be decoded in parallel.In another example, the first set of occupancy codes for the first setof nodes is decoded using a first coding mode and the second set ofoccupancy codes for the second set of nodes is decoded using a secondcoding mode.

The first coding mode and the second coding mode can use any of a depthfirst coding order, a breadth first coding order, a predictive geometrycoding technique and the like. In some examples, the coded bitstreamincludes a first index that is indicative of the first coding mode forthe first sub octree and a second index that is indicative of the secondcoding mode for the second sub octree.

In another embodiment, the first node and the second node are of aspecific node size for coding order change. In some examples, largernodes in the nodes are coded using a first coding order, and smallernodes in the nodes are coding using a second coding order. The nodesizes of the larger nodes are larger than a specific node size forcoding order change. The node sizes of the smaller nodes are equal orsmaller than the specific node size for coding order change. In anexample, the first coding order is breadth first coding order and thesecond coding order is depth first coding order. In another example, thefirst coding order is depth first coding order and the second codingorder is breadth first coding order.

In some examples, the specific node size for coding order change isdetermined based on a signal in the coded bitstream for the point cloud.In some examples, the signal is provided when a control signal isindicative of a change of coding order.

At (S1730), the octree structure can be reconstructed based on thedecoded occupancy codes for the nodes.

At (S1740), the point cloud is reconstructed based on the octreestructure. Then, the process proceeds to (S1799) and terminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 18 shows a computersystem (1800) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 18 for computer system (1800) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1800).

Computer system (1800) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1801), mouse (1802), trackpad (1803), touchscreen (1810), data-glove (not shown), joystick (1805), microphone(1806), scanner (1807), camera (1808).

Computer system (1800) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1810), data-glove (not shown), or joystick (1805), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1809), headphones(not depicted)), visual output devices (such as screens (1810) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1800) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1820) with CD/DVD or the like media (1821), thumb-drive (1822),removable hard drive or solid state drive (1823), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1800) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1849) (such as, for example USB ports of thecomputer system (1800)); others are commonly integrated into the core ofthe computer system (1800) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1800) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1840) of thecomputer system (1800).

The core (1840) can include one or more Central Processing Units (CPU)(1841), Graphics Processing Units (GPU) (1842), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1843), hardware accelerators for certain tasks (1844), and so forth.These devices, along with Read-only memory (ROM) (1845), Random-accessmemory (1846), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1847), may be connectedthrough a system bus (1848). In some computer systems, the system bus(1848) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1848),or through a peripheral bus (1849). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1841), GPUs (1842), FPGAs (1843), and accelerators (1844) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1845) or RAM (1846). Transitional data can be also be stored in RAM(1846), whereas permanent data can be stored for example, in theinternal mass storage (1847). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1841), GPU (1842), massstorage (1847), ROM (1845), RAM (1846), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1800), and specifically the core (1840) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1840) that are of non-transitorynature, such as core-internal mass storage (1847) or ROM (1845). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1840). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1840) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1846) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1844)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for point cloud coding, comprising:receiving point cloud data of a point cloud; deriving an octreestructure of the point cloud based on the point cloud data, nodes in theoctree structure corresponding to three dimensional (3D) partitions of aspace of the point cloud, sizes of the nodes being associated with sizesof the corresponding 3D partitions, the nodes in the octree structureincluding first nodes having first sizes larger than a threshold nodesize for coding order change, and second nodes having second sizes equalto or smaller than the threshold node size for coding order change, thesecond nodes being arranged into one or more sub octrees; generating, byprocessing circuitry of an apparatus, a sequence of occupancy codes forthe nodes in the octree structure of the point cloud, the sequence ofoccupancy codes includes: a first portion of the sequence of occupancycodes for the first nodes arranged according to a first coding order,and a second portion of the sequence of occupancy codes including one ormore subsets of occupancy codes for the one or more sub octreesrespectively arranged according to a second coding order, the secondcoding order being different from the first coding order; encoding, bythe processing circuitry of the apparatus, the sequence of occupancycodes into encoded data; and generating, by the processing circuitry ofthe apparatus, a coded bitstream that includes the encoded data.
 2. Themethod of claim 1, wherein the one or more subsets of occupancy codesfor the one or more sub octrees comprise: a first subset of occupancycodes for a first sub octree with a first node being a root of the firstsub octree, and a second subset of occupancy codes for a second suboctree with a second node being a root of the second sub octree, thefirst node and the second node having a same node size.
 3. The method ofclaim 2, wherein the generating the sequence of occupancy codescomprises: generating the first subset of occupancy codes for the firstsub octree in parallel with generating the second subset of occupancycodes for the second sub octree.
 4. The method of claim 2, wherein theencoding the sequence of occupancy codes comprises: encoding, using afirst coding mode, the first subset of occupancy codes for the first suboctree; and encoding, using a second coding mode, the second subset ofoccupancy codes for the second sub octree.
 5. The method of claim 4,wherein the coded bitstream includes a first index that is indicative ofthe first coding mode for the first sub octree and a second index thatis indicative of the second coding mode for the second sub octree. 6.The method of claim 1, wherein the first coding order is a breadth firstcoding order and the second coding order is a depth first coding order.7. The method of claim 1, wherein the first coding order is a depthfirst coding order and the second coding order is a breadth first codingorder.
 8. The method of claim 1, wherein the coded bitstream includes asignal indicating the threshold node size for coding order change.
 9. Anapparatus for point cloud coding, comprising: processing circuitryconfigured to: receive point cloud data of a point cloud; derive anoctree structure of the point cloud based on the point cloud data, nodesin the octree structure corresponding to three dimensional (3D)partitions of a space of the point cloud, sizes of the nodes beingassociated with sizes of the corresponding 3D partitions, the nodes inthe octree structure including first nodes having first sizes largerthan a threshold node size for coding order change, and second nodeshaving second sizes equal to or smaller than the threshold node size forcoding order change, the second nodes being arranged into one or moresub octrees; generate a sequence of occupancy codes for the nodes in theoctree structure of the point cloud, the sequence of occupancy codesincludes: a first portion of the sequence of occupancy codes for thefirst nodes arranged according to a first coding order, and a secondportion of the sequence of occupancy codes including one or more subsetsof occupancy codes for the one or more sub octrees respectively arrangedaccording to a second coding order, the second coding order beingdifferent from the first coding order; encode the sequence of occupancycodes into encoded data; and generate a coded bitstream that includesthe encoded data.
 10. The apparatus of claim 9, wherein the one or moresubsets of occupancy codes for the one or more sub octrees comprise: afirst subset of occupancy codes for a first sub octree with a first nodebeing a root of the first sub octree, and a second subset of occupancycodes for a second sub octree with a second node being a root of thesecond sub octree, the first node and the second node having a same nodesize.
 11. The apparatus of claim 10, wherein the processing circuitry isconfigured to: generate the first subset of occupancy codes for thefirst sub octree in parallel with generating the second subset ofoccupancy codes for the second sub octree.
 12. The apparatus of claim10, wherein the processing circuitry is configured to: encode, using afirst coding mode, the first subset of occupancy codes for the first suboctree; and encode, using a second coding mode, the second subset ofoccupancy codes for the second sub octree.
 13. The apparatus of claim12, wherein the coded bitstream includes a first index that isindicative of the first coding mode for the first sub octree and asecond index that is indicative of the second coding mode for the secondsub octree.
 14. The apparatus of claim 9, wherein the first coding orderis a breadth first coding order and the second coding order is a depthfirst coding order.
 15. The apparatus of claim 9, wherein the firstcoding order is a depth first coding order and the second coding orderis a breadth first coding order.
 16. The apparatus of claim 9, whereinthe coded bitstream includes a signal indicating the threshold node sizefor coding order change.
 17. A non-transitory computer-readable mediumstoring instructions which when executed by a computer for videodecoding cause the computer to perform: receiving point cloud data of apoint cloud; deriving an octree structure of the point cloud based onthe point cloud data, nodes in the octree structure corresponding tothree dimensional (3D) partitions of a space of the point cloud, sizesof the nodes being associated with sizes of the corresponding 3Dpartitions, the nodes in the octree structure including first nodeshaving first sizes larger than a threshold node size for coding orderchange, and second nodes having second sizes equal to or smaller thanthe threshold node size for coding order change, the second nodes beingarranged into one or more sub octrees; generating a sequence ofoccupancy codes for the nodes in the octree structure of the pointcloud, the sequence of occupancy codes includes: a first portion of thesequence of occupancy codes for the first nodes arranged according to afirst coding order, and a second portion of the sequence of occupancycodes including one or more subsets of occupancy codes for the one ormore sub octrees respectively arranged according to a second codingorder, the second coding order being different from the first codingorder; encoding the sequence of occupancy codes into encoded data; andgenerating a coded bitstream that includes the encoded data.
 18. Thenon-transitory computer-readable medium of claim 17, wherein the one ormore subsets of occupancy codes for the one or more sub octreescomprise: a first subset of occupancy codes for a first sub octree witha first node being a root of the first sub octree, and a second subsetof occupancy codes for a second sub octree with a second node being aroot of the second sub octree, the first node and the second node havinga same node size.
 19. The non-transitory computer-readable medium ofclaim 17, wherein the first coding order is a breadth first coding orderand the second coding order is a depth first coding order.
 20. Thenon-transitory computer-readable medium of claim 17, wherein the firstcoding order is a depth first coding order and the second coding orderis a breadth first coding order.